1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus such as used i nan R-DAT (rotary head-digital audio tape deck). In particular, it relates to the extraction of a synchronizing signal.
2. Background of the Invention
In a recently standardized R-DAT, a pilot signal and a synchronizing signal for detecting the pilot signal are recorded in each inclined track by a rotary magnetic head so as to perform tracking for the inclined track. A pilot signal level (a crosstalk component) produced from a right adjacent track is detected when the synchronizing signal is detected. Also, a pilot signal level (a crosstalk component) produced from a left adjacent track after a predetermined time has passed from the point in time of detecting the synchronizing signal to be zero is detected. These two detected levels are compared to produce a tracking error signal on the basis of a difference between the detected levels.
In order to detect such a synchronizing signal, a device as shown in FIG. 1 is considered such as is a possibility. That is, the synchronizing signal, which is pulse-coded and recorded on a magnetic tape and which has a pattern such as that shown in FIG. 2(a), is reproduced by a magnetic head 1 which traces the inclined track while it is rotating. The magnetic head 1 constitutes a kind of a differentiation circuit, and produces an output signal as shown in FIG. 2(b). The output signal is applied to an integrating circuit 2 to be integrated therein to be restored into the original signal as shown in FIG. 2(c). The restored signal is applied to a comparator 3 to be compared with a predetermined reference level (zero level) so as to be shaped into a signal such as is shown in FIG. 2(d). The shaped signal is applied to a counter 4 which acts as a reading circuit. The counter 4 counts the number of pulses in the input signal, and produces a detection signal indicating that the synchronizing signal has been detected when the number of counts reaches a predetermined numerical value, for example, 20.
The just-described device, being arranged merely to count an output signal of the magnetic head 1 by the counter 4 through the integrating circuit 2 and the comparator 3, has a disadvantage in that the device is poorly protected against noise. For example, in a system in which no exclusive erasing head is provided and old information is erased by over-writing new information on top of the old information, there is a disadvantage in that an old synchronizing signal corresponding to the old information is not sufficiently erased because of its relatively low frequency so that the old synchronizing signal is erroneously detected, making correct tracking control impossible.